I think a fun idea is the ability to improve the player character with cyborg additions or some zombie/mutant gene mods. Right now you can upgrade your character by adding powerlegs and armor, you make the electrified knife to upgrade your basic knife attack, and you boost your health by eating canned meat. However, I think it'd be way cooler and thematically appropriate to do things like necrotizing your flesh to gain increased maximum hp and bonus health from canned meat, weld those empty cans directly on your dermal armor to patch up the holes, and grow some extra giant spider limbs to increase movment speed and melee damage. It'd be great to progress your character in more ways than simply having the most guns, and if the self-modifications were exclusionary or hard to get more than one of then they could have reasonably large bonuses to create alternate playstyles.

In Teleglitch, you fight against monsters. Why not become one? /overdrama What do you think would be some fun modifications that would fit with Teleglitch lore?

This would actually make a pretty cool mod. First find out how to make an item you pick up(craft, whatever) not appear in your inventory. Like how armor and ammo in your inventory immediately goes into your cache instead of sticking around.

Second, and I think would be the harder part, make it so when you apply these items, it changes your character sprite to look more metallic, have extra legs or arms, etc.

I think this would fit existing lore pretty well. The people behind all of these experiments were also looking into immortality and bodymods on still-living creatures, so why not show some of their success? You're already an uber-smart crafter, why not extend that to the rest of Teleglitch lore?